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Supply requirement for heaters

whjohnson

Been asked to look at provision of a new supply for  a 72KW TPN blow heater. Am getting current per phase coming in at over 100A with a cable size of 35mm 4 core. Having taken this as correct, am now looking at a 36KW option instead. Current is coming in at around 52A with a cable size of either 10mm 4 core or 16mm 4 core. I don't know anything else at the moment until I visit the site next week, but am not confident that these valuses are correct for the KW ratings.

Have assumed a pf of 1 for resistive load. Don't know how the elements are configured in the heater and am guessing the neutral is required for the fan motor and controls.

Input gratefiully recieved..

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    am not confident that these valuses are correct for the KW ratings.

    My calculations give 104.3A and 52.2A - so in agreement with yours I think. I also notice that web site suggests a 125A extension lead to be used with the 72kW version - so that stacks up as well.

       - Andy.

  • 0 in reply to AJJewsbury

    I agree with Andy. The instruction manual suggests that a further 4.5 kW are required for the fan. It also states a "rated current" of 110 A. I agree that 35 mm² cable would be required.

    The 36 kW model has a rated current of 57 A.

    I find it a little odd that the heating capacity is given for a certain floor area when surely, the volume of the space would seem to be more appropriate.

  • 0 in reply to Chris Pearson

    I find it a little odd that the heating capacity is given for a certain floor area when surely, the volume of the space would seem to be more appropriate.

    The heating world seems to be full of approximations and rules of thumb (e.g. x sized boiler for a n bedroom house). If you're talking about heating an ideal empty space, then yes, the volume of the air might be about the main factor to consider. But if you were talking about keeping a volume warm, the area of the envelope that contains it (and the thermal resistance of that envelope) would be much more significant. Real world would be some complicated mix of the two approaches (and probably an acceptable warm up time, and weather conditions as well).

    I guess most of the time people just want a bit of advise from someone who's done this sort of thing before - e.g. the "big one" is usually OK a for medium size marquee, the "very big one" for anything much larger ... maybe the floor area is just an approximation of that kind of approximation?

       - Andy.

  • 0 in reply to AJJewsbury

    In this instance, the heaters seem to be required only for initial heating. Once you get plenty of people in a space, they will generate their own heat.

    It occurs to me that the height of a space might be proportional (or thereabouts) to the floor area, so the approximation may be reasonable.

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  • 0 in reply to AJJewsbury

    In this instance, the heaters seem to be required only for initial heating. Once you get plenty of people in a space, they will generate their own heat.

    It occurs to me that the height of a space might be proportional (or thereabouts) to the floor area, so the approximation may be reasonable.

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